DSC investigations of the phase transitions of [M(NH3)6](ClO4)2 and [M(NH3)6](BF4)2, where M = Co and Cd

Solid polymorphism of four compounds of the type [M(NH3)(6)](XY4)(2), where M = Co2+ or Cd2+, and XY4 = ClO4- or BF4- has been studied at 100 - 300 K by DSC. One or two phase transitions of the investigated compounds have been found. For the compounds with M = Co the phase transitions have not yet been described in the literature. For the compounds with M = Cd the phase transition-temperature is in good agreement with the results obtained by NMR and EPR, Generally, for [M(NH3)(6)](BF4)(2) compounds (M = Mg, Fe, Co, or Ni) the phase transition temperature T-Cl is lower than that for the corresponding [M(NH3)(6)](ClO4)(2). but for compounds with M = Cd it is higher. However, the enthalpy and entropy changes at the T-Cl phase transitions of [M(NH3)(6)](BF4)(2) are always lower than those for [M(NH3)(6)](ClO4)(2). Moreover, for the compounds of this type a correlation between the transition temperature To and the crystal lattice parameter a has been found.